Because of low power consumption property, liquid crystal displays (LCDs) have become very popular and suitable for all kinds of electronic devices. The main principle of LCD is to control the light transmission properties of liquid crystal through an electrical field so as to display images.
A liquid crystal display comprises an array substrate, a color filter substrate, and a liquid crystal layer disposed therebetween. As illustrated in FIG. 1, the array substrate generally comprises a plurality of gate lines (gate lines G1-G4) and a plurality of data lines (data lines D1-D8). A sub-pixel region is defined by a gate line and a data line that intersect with each other, a thin film transistor 10 and a pixel electrode 11 are configured in each sub-pixel region, in this way, a sub-pixel is obtained. The thin film transistor 10 comprises a gate electrode G, a source electrode S and a drain electrode D; the gate electrode is electrically connected to the gate line, the source electrode is electrically connected to the data line, and the drain electrode is electrically connected to the pixel electrode. Taking vertical electric field type liquid crystal display as an example, a common electrode is configured on the color filter substrate, an electrical field is generated when applying voltages to the pixel electrode and the common electrode. The magnitude of the electrical field generated between the pixel electrode and the common electrode determines the rotation degree of the liquid crystal molecules. Therefore, the rotation degrees of the liquid crystal molecules can be changed through adjusting the magnitude of the electrical field between the pixel electrode and the common electrode, and then the gray scale of the display device can be presented.
The pixel electrode and the common electrode are generally called as driving electrodes; generally speaking, the common electrode voltage is kept constant, therefore, the polarity of the driving electrode is determined compared with the common electrode. The polarity of the driving electrode is positive when the pixel electrode's voltage is higher than the common electrode's voltage, and the polarity of the driving electrode is negative when the pixel electrode's voltage is lower than the common electrode's voltage. Only is the rotation direction of the liquid crystal molecules affected when the polarity of the driving electrode is inversed, but the transmittance of the liquid crystal layer is determined by the electrical field value between the common electrode and the pixel electrode.
For example, the polarity of the driving electrode is positive when the common electrode voltage is 1V and the pixel electrode voltage is 3V; the polarity of the driving electrode is negative when the common electrode voltage is 1V and the pixel electrode voltage is −1V. In addition, the rotation degree of the liquid crystal molecules (i.e., transmittance of the liquid crystal layer) is kept the same for the above-mentioned two voltages of the pixel electrode.
In display operations, irreversible damages can be caused if the liquid crystal molecules of an LCD continue working under a single polarity in a long time period. Therefore, it is necessary to inverse the polarity between the driving electrodes periodically, i.e., alternate between the positive polarity and the negative polarity. Polarity inversion can be conducted by means of frame inversion, row inversion, column inversion, dot inversion and so on. Compared with frame inversion, row inversion and column inversion, dot inversion can further ensures normal rotation/orientation of the liquid crystal molecules for long operation time.